Sensitizing of photographic emulsions



Feb. 23, 1937. w, zEH ET AL 2,071,374

I SENSITIZING OF PHOTOGRAPHICVEMULSIONS Filed July a, 1932 wuwntom Patented Feb. 23, 1937 UNITED STATES PATENT OFFICE SENSITIZIN G F PHGTUGRAPHIC MULS IONS v of New York Application July 8, 1932, Serial No. 621,474

In Germany July 11, 1931 n Claims.v

Our present invention relates to sensitizing of photographic emulsion.

One of its objects is to provide such an emulsion the sensitivity of which is raised over the range of wave lengths to which the emulsion is normally sensitive. Further objects will be seen from the detailed specication following hereafter.

Reference is made to the accompanying drawing in which there are represented a few spectrograms of the same emulsion sensitized with our sensitizers. o

Fig. 1 shows for the sake of comparison the spectrogram of the unsensitized silver bromide emulsion containing about 4% of silver iodide used for the tests.

Fig. 2 shows the spectrogram of the emulsion sensitized with bis- [3-ethylanthraceno2.1 :4.5- thiazoie-(Z) l--ethyl trimethine cyanine bromide,

Fig. 3 that of the emulsion sensitized with bis- [3 ethyl carbazolo 3'.2:4.5 thiazole (2) 1- trimethine-cyanine-chloride.

Fig. 4 that of the emulsion sensitized with bis- [3 ethyl acenaphtheno 5.4':4.5 thiazole (2)]--methyl-trimethine-cyanine bromide and Fig. 5 that of the emulsion sensitized with bis- [3 methyl diphenyleneoxide 2'.3 :4.5 thiazole-(2) l--methyl-trimethine-cyanine chloride.

We have found that the thiocarbocyanines which derive from higher polynuclear cyclic compounds are well suitable for sensitizing to red and have over the hitherto known trimethinecyanines the advantage of a higher intensity in the red of the spectrum.

As a starting material for the new sensitizing dyestuis there mayl be used the 2methyl thiazole of anthracene phenanthrene Y GHz-CHI acenaphthene C Hl iluorene CH=CH chrysene carbazoie diphenylenooxido The. dyestuiis are obtainable analogous to known methods. In order to prepare, for instance, the anthraceno-thiazole-trimethine-cyanines, one starts from alphaor -anthramine and, by way of its .acetyl- `and thioacet-compound, the 2-methylanthra thiazole is obtainable by oxidation with potassium ferricyanide. By treating the Z-methylanthrathiazole with diethylsulphate or ethyltoluene-sulphonate in known mannerv it is transformed into the quaternary compound which is then condensed in anhydrous pyridine to form a trimethine-cyanine by means of a trialkylorthocarboxylic acid ester. When condensing anthrathiazole with an alkylorthoformic ester there may be obtained carbocyanines of the following formulae (wherein R stands for an alkyl radical and X for an acid anion) alpha compound H B E .la-i N Ii' the condensation is carried out with the ester of a higher orthocarboxylic acid the hydrogen of the central C-atom of the chain is substituted by an alkyl group. The dyestuiIs substituted in this manner possess a more intensive sensitizing action, the compounds having a hydroxyalkyl substituent showing a better solubility in water. The scope of the invention is intended to include also such dyestufl's as are substituted in any manner in the anthracene etc. rings or in which the sulphur of the thiazole ring has been replaced by oxygen or selenium.

'I'he new sensitizing dyestufls are added to the emulsion in the usual concentrations (about 5 to 100 mgms. per kilo oi emulsion) or are incorporated by the bathing process. The best amount can easily be determined by, a few experiments. 'Ihey are particularly suited for the manufacture of panchomatic emulsions.

'Ihe following examples serve to illustrate our 45 invention more clearly. Examples 1 and 2 instance the manufacture of the bases our sensi-v tizers are made from, the method of preparation being like that of the dyes analogous to known methods. Examples 3- to 8 demonstrate the' igianufacture of the dyes when starting from the Example 1. 2 methylcarbazolethiazole prepared as follows:

9-benzoyl-3-amino-carbazole (melting vpoint 14s zo 150 c. is transformed into 9-benmy1-2- NJKCH:

and forming when recry-stallized from diluted 5 alcohol colorless crystals whichj melt at 165 C.

Example 2.-4For producing 2 methyldi phenyleneoxide-thiazole 2-amino-diphenyleneoxide is converted by the method described in U. S. Patent 1,788,297 into the amino-thiazole which crystallizes from hot diluted hydrochloric acid in the form of the chloride. By cleaving the molecule in an alkaline medium by the method described in U. S. Patent 1,788,297 the o-mercapto-2-amino-diphenyleneoxide is separated in form of' its zinc mercaptide. When heated with acetic anhydride and glacial acetic acid this compound yields the Z-methyl-thiazole corresponding probably to the following formula:

and forming when recrystallized from diluted alcohol glittering crystals which melt at 162 C.

The bases may be converted into their quaternary ammonium-salts according to known general methods. For instance, the dlethyl-sulfate is obtainable by heating the base and diethylsulfate for a short time, say about 10 minutes to about 130 C. 'Ihe ethiodides of the bases may be obtained by boiling the base with ethyl iodide i'or a long time or by heating the base with ethyl iodide in a bomb tube to about C. I

Example 3.--The dye bis'- [3-ethyl-anthraceno- 2.l' :4.5-thiazole- (2) -ethyl trimethine cy aulne-bromide corresponding probably to the formula:

pyridine with 5 cc. of tri-ethyl ortho propionate for about 1/2 hour to about 130 C. Hereon the dye is precipitated by addition of about 100 cc.

of a 5 per cent solution of .potassium bromide. By recrystallization from methanol a blackishgreen crystalline powder is obtainable.

'I'he alcoholic solution of the dye has an absorption maximum at a wave length of about 610W. A silver bromide emulsion containing about 4 per cent of silver iodidewhen sensitized with the dye acquires a sensibility to wave lengths of about .E20-720ML with a maximum at about 640ml..

Example 4.-The dye bis-[3-ethyl-anthraceno- 1.2 :4'5-thiazole-(2) l- -ethyl trimethine cy aulne-bromide is produced by starting from 2- methyl-a-anthrathiazcle-diethylsulfate, the reaction and lthe conditions being the same as in Example 3.

Example 5.-'rhe dye bis-[s-e'thyl-carbazol 3'.2' :4.5-tliiazole-(2) lp ethyl trimethine-cy aulne-chloride corresponding to the formula:

i N g N 02H8 C] xm is obtainable as follows;

5 grams of Z-methylcarbazole-diethyl-sulfate are heated with 3 cc. of ethyl ortho formate in 10 cc. of pyridine for about 1/2 hour to 130 C. On the addition of sodium chloride the dye is precipitated from the blue solution. Recrystallization from methanol yields green little rods.

The alcoholic solution of the dye shows an absorption maxim at a wave length of about 605ml. A silver br mide emulsion containing 'about 4 per cent of-silver iodide when sensitized with the dye acquires a sensibility for waves of 'about 510ml. to about '110ml with' a maximum Example 6.-The dye bis-IS-ethyI-acenaphtheno,5.'4: 4.5-thiazole-(2) lp methyl trimethine-cyanine-bromide corresponding to l the formula:

is obtainable by heating 3 grams of 2-methyl-aoenaphthenethiazole-diethylsulfate in I cc. of dry 4 pyridine with 3 cc. of ethyl ortho acetate for sorption maximum at about 585ml.

about 1/2 hour to 130 C. I'he dye is precipitated by adding to the reaction mixture about 100 cc. of a 5 per cent solution of potassium bromide. After recrystallization from methanol it forms small blue felted needles. y

The alcoholic solution of the dye has an ab- A silver bromide emulsion containing about 4 per cent of silver iodide when sensitized with the dye yac quires a sensitiveness for wave lengths of about 500ml to about 710ml with a maximum at about Example 7.-'I'he dye bis-'[3-ethyl-dipheny1- eneoxide-Z' 3':4 .'5thiazole-(2)]pmethyltri methine-cyanine-chloride corresponding to the formula may be producedby heating' 2.5 grams of diphenyleneoxide-2-methylthiazole and 4 cc. of ethyl-ortho-acetate with cc. of pyridine for about V2 hour to 130 C. Thedye which precipitated already during the heating operation'in the form of its sulfalkylate is separated from ythe mother liquid by suction. The dye is .then dissolved in methanol and precipitated by addition of a 10 per cent solution of common salt.

The alcoholic solution of the dye 'shows an absorption maximum at a waveV length of about 585m. A silver bromide emulsion containing about 4 per cent of silver iodide when sensitized with the dye acquires a sensibility to wave lengths of about 510W to about 690W. with a maximum at about 615ML.

The dyes are yobtainable according to the desired solubility in .form of the bromide', iodide, perchlorate, etc., and are used in a'quantity such as is usual for the known sensitizing dyes. This quantity may amount to about l0 to 50 milligrams per 1 kilo of emulsion ready for being cast, which contains about 9 per cent of gelatin and 4.5 per cent of silver halide, the rest being water. However, the invention is not limited to the quantities just indicated and the most suitable amount can in each case 'be found by a few comparative experiments. 'Ihe dyes may be added to the emulsion in form of solutions; suitable solvents are the alcohols, for instance, methyl or ethyl alcohol, which may be used in anhydrous form or diluted with water. The dyes may be applied to .the emulsion during any stage of its production but are preferably added to thenished vemulsion before it is cast.

For example, to 1 kilo of a liquid emulsion ready for being cast there are added 30 milligrams of 1.l'diethyl--anthrathio-mesoethyl-carbocyanine-bromidedissolved in 120 cc. of methanol or alcohol, while thoroughly stirring. After the photographic material in a solution of the dye. A

Such a treatment may be as follows: The photographic materialto be sensitized is bathed in a solution containing 1 milligram of 1.1'diethyl anthrathiomesoethyl-carbocyanine-bromide in 50 parts of an aqueous solution of methanol of 50 per cent strength for about 5 `minutes and is then 35 dried; itis then ready for use.

The dyes are suitable for sensitizing sion made according to the boiling process, as well as for sensitizing an emulsion made according to the ammonia process.

It is to be understood that our invention is not limited to the foregoing examples or to the speciilc details given therein. Numerous other embodiments are possible and we contemplate as included within our invention all such modifications and equivalents as fall within the. scope u'of the appended claims. So, for instance, the different nuclei may contain one or more substituents. The nomenclature used is arbitrary, but it is familiar to every chemistsldlled in the art and has the advantage of clearness. mulae of the dyes as -given herein represent the molecular structure of our new dyes so far as known. If,` however, in future it should become evident that the formulae do not exactly correspond to-the dyes this fact will not aiect our invention since the dyes will be easily identified by the method of producing the same Awhich has been fully described in the examples and is analogous to known methods.

What we claim is: l

1. A. photographic material comprising a silver halide emulsion containing a dye selected from the group consisting of bis-[3-alkyl-anthraceno,' phenanthreno, fluoreno, chryseno and acenaphtheno-thiazole- (2) l-trimethine-cyanine salts.

2. A photographic material comprising a silver halide emulsion containing a dye selected from thegroup consisting of bls-[3-alkyl-anthraceno, phenanthrenmiluoreno, chryseno and acenaphtheno-thiazole-(2) l--alkyl-trimethine cyanine salts.-

3. A photographic material comprising a silver halide emulsion containing bis- [3-ethyl-acenaphtheno-5A': 4.5-thiazole- (2) l--methyl-trimethan em'lll- The fory ine-cyanine bromide corresponding with the formula:

1' l 4'5 El; H on. anni 5. A photographic material comprising a silver halide emulsion containing bis-[3-ethyl-anthraceno-2'.1: -thiazole- (2) l--ethyl-trimethlnecyanine-bromide corresponding probably to the formula 4. A photographic material comprlsinsya. silver halide emulsion containing bis-[3-ethyl-anthraceno-1'2': 4.5-thiazole- (2) ]ethyltrimethine 

